Isolated rat myocytes will be employed to assess the role of alpha adrenergic receptors in the control of myocardial metabolic process - in particular glycogenolysis and amino acid transport. The contribution of alpha- vs. beta-adrenergic receptors in mediating these metabolic effects of catecholamines will be assessed by the use of a variety of agonists (isoproterenol: predominantly beta; epinephrine: mixed; phenylephrine: predominantly alpha) in the presence and absence of specific antagonists (propranolol: beta and phentolamine, phenoxybenzamine or dehydroergotamine: alpha). The role of calcium ion in these processes will also be investigated by altering both extracellular concentration and flux (employing transport inhibitors, e.g., verapamil; and accelerators, e.g., the ionophore A23187). In addition, changes in ion flux (sodium, potassium, calcium) in response to catecholamines will be measured employing appropriate radiolabeled ions. We also plan to determine alpha and beta receptor site number (density) in intact myocardium as well as isolated myocytes by the use of high specific activity radiolabeled catecholamine agonists and/or antagonists.